The present invention relates to a welding method and apparatus, and more particularly to a method and apparatus for automated welding of tubes for use in brachytherapy.
In the treatment of various cancers, and in particular prostate cancer, a process called brachytherapy has proved effective. In brachytherapy, small capsules containing radioactive material are implanted in or near to the tumour.
One known form of capsule or canister, commonly used to treat prostate cancer and referred to as a xe2x80x9cseedxe2x80x9d, is shown in FIG. 7. The capsule 100 comprises a silver rod 102, coated with a radioactive isotope of iodine such as I-125, inside a hollow titanium tube 104. The ends of the tube are welded closed. Resin balls coated with radioactive iodine can be used instead of the silver rod 102. The completed capsule has a width of approximately 1.0 mm and a length of approximately 4.5 mm. The capsules or seeds can be implanted into a patient individually; alternatively, the capsules can be inserted into medical stitching material or suture, which is then inserted into the prostate and left there.
The number of capsules implanted into each patient obviously varies in accordance with the regime of treatment required, but is commonly in the region of 50 to 100. The capsules are normally made by hand, with the welding process used to close the ends of the tube being carried out manually. It will be appreciated that making such a large number of capsules for each patient by hand takes considerable time and expense.
According to a first aspect of the invention, there is provided an automated method of welding closed one end of each of a multiplicity of open-ended tubes suitable for use in the manufacture of brachytherapy capsules, which comprises repeating the steps of loading each tube into a holder, bringing the tube in the holder to a welding station, welding closed one end of the tube, and releasing the welded tube from the holder.
With such a method, a large number of tubes can be processed relatively quickly.
Preferably, the step of loading each tube into a holder comprises the steps of orientating the tubes into a particular orientation in a feeder, and feeding each tube from the feeder to a holder. Once orientated in the feeder, the tubes can be fed to the holder in a desired orientation. Manual picking up and orientation of the tubes is avoided.
As the tubes are for use in making brachytherapy seeds, they will be of a suitable size for brachytherapy implantation, for example, a few millimetres long by about one millimetre wide. The tubes are typically a little longer than the product brachytherapy seed, since it is usual for some of the tube material to be used to form the weld closure.
The welding of one end of the tube closed is preferably effected by melting the material of the tube such that the melted material forms the end closure. Preferably, no additional material is required.
Closure of the remaining open end of the tube will be effected after the active substance for brachytherapy has been inserted.
In general, the tubes to be welded will be formed by being cut from a long length of tubing, and having been so cut they will be randomly orientated. According to the method of the invention, the tubes are orientated in the feeder, so that each tube is ready to be fed to a holder. A preferred method comprises agitating the tubes in order to orientate them in the feeder.
Various ways may be used to control feeding of each tube to a holder. For example each tube may be individually picked up by a robot arm and placed in the holder. Preferably, the method comprises arranging the tubes end to end one above another in the feeder, urging a restraining member against a side of the lowermost-but-one tube to prevent it from downward movement, and releasing the lowermost tube from the feeder individually to the holder. The restraining member thus engages the lowermost-but-one tube and in so doing all the tubes above are held in position, allowing the lowermost tube to be individually released. After release, a blocking member is preferably moved into a blocking position below the tubes and the restraining member is retracted to allow the tubes to drop down, the then lowermost tube being stopped by the blocking member. The restraining member can then be advanced against the now lowermost-but-one tube and the feeding cycle is then repeated.
In a preferred method, the holder receives a tube, conveys the tube to the welding station, and releases the tube, said holder moving in a closed loop.
The provision of a holder which moves in a closed loop facilitates the automation of the welding process. The tube to be welded is supplied to the holder in a particular orientation. The tube is then carried to the welding station where it is welded. The welded tube is released, preferably at an ejection station to which it is carried from the welding station. Since the holder moves in a closed loop, it comes back to its original position, and the procedure can then be repeated.
It is possible to use one holder, although the rate of production of such an apparatus is low, as it can only operate on a single tube at a time. Accordingly, it is preferred that a plurality of said holders are provided. This allows greater productivity.
The welding of the end of each tube obviously requires high temperatures in order to melt the metal of the tube. It is possible for these high temperatures to cause damage to whatever is holding the tube during the welding operation, particularly if repeated welding operations are carried out. Some form of cooling can be provided to reduce the risk of damage. However, in a preferred method, the holders move through said welding station sequentially, each of the plurality of holders cooling between successive welding operations while the other holders move through the welding station. This ensures that after each of the holders holds a tube while it is being welded, it cools down before it next holds a tube being welded. This reduces the risk of heat damage to the holders.
Many possible methods of moving the or each holder through the welding station can be employed. For example, each could be individually driven along a track. However, in a preferred method, the or each holder is mounted at the periphery of a rotatable member. Receiving, welding and releasing stations may conveniently be provided at successive points along the rotational path of the holder. Where a plurality of holders are provided they can all be mounted by the rotatable member, with the advantage of simplicity, as it is then only necessary to provide a single drive means.
The holder may for example be a cavity into which the tube can be dropped by the feeder and which restricts movement of the tube adequately during welding. Preferably, however, the holder adopts an open condition when receiving and releasing a tube and a closed condition to grip the tube firmly at least during welding of the tube. This arrangement assists the receiving and releasing steps, whilst properly holding the tube during welding.
The holder may be in the closed condition at all times except when receiving and releasing a tube. However, the method preferably comprises causing the holder to move from the open condition to the closed condition when the holder is at the welding station. Thus, means can be provided at the welding station for causing the closing action, rather than such means being provided as part of the holder itself. This can advantageously simplify the design of the holder, which is particularly advantageous where the holder is conveyed from one processing station to another, e.g. by a rotatable member.
Viewed from another aspect the invention provides an automated method of welding closed one end of each of a multiplicity of open-ended tubes suitable for use as brachytherapy capsules, comprising repeating the steps of feeding each individual tube to a holder in an open condition, conveying the holder in the open condition to a welding station, causing the holder to close and grip the tube firmly by means of a holder actuator provided at the welding station, and welding one end of the tube closed. The holder actuator is advantageously not conveyed with the holder but instead is provided at a fixed location at the welding station.
The holder may have a floor portion for preventing downward movement of the tube during conveyance. However, this is not necessary and the method preferably comprises sliding the tube on a slide plate during conveyance of the holder. It has been found, contrary to expectations, that the lower ends of the tubes are not damaged as a result of sliding along the slide plate.
Thus, as long as the tubes are of uniform lengths, the top end of the tube will always be the same height above the slide plate. Provided the welder is also fixed in position, the distance between the upper end of the tube and the welding unit will remain constant. This can ensure that the tube is in the correct position for welding. Thus it is strongly preferred that the multiplicity of tubes for use in the preferred embodiment of the present invention are of uniform length.
It is possible for the welded tubes (also referred to as xe2x80x9ccansxe2x80x9d) to be removed from the holders by being picked out, either by hand or by providing a further piece of apparatus to carry out this step. However, it is preferred that the slide plate be provided with a cut-out region, allowing cans to fall past the slide plate. The cans are then removed from the holders by the force of gravity. A preferred method therefore comprises conveying the welded tube to a release position where the slide plate is provided with a cut-out region, allowing the can to fall through the cut-out region.
The holder can take a number of forms, as long as the tube is held correctly. For example, the tube could be held in an inflatable collar, which is normally deflated and can be inflated when it is necessary to hold the tube tightly. However, it is preferred that said holder is in the form of a pair of jaws which are biassed to an open position and can be selectively closed. This allows the tube to be inserted into the holder when they are in their open position, where the spacing between the jaws is relatively wide, and so facilitates insertion of the tube. This also allows for release of the tube by opening the jaws.
It is possible for the jaws themselves to be provided with means allowing them to be closed tightly around the tube. For example, a solenoid or a pneumatic cylinder could have its ends attached to the halves of the jaw, and would then be able to open or close the jaws e.g. at the welding station. However, as described above, a holder actuator is preferably provided at the welding station to close the jaws. This simplifies the construction of the jaws, and, where a plurality of sets of jaws are provided, involves the provision of just one holder actuator, rather than one for each set of jaws.
In a preferred method, the holder is in the form of a block slidably mounted in a recess in a holder support, said block being biassed outwardly by resilient means, e.g. compression springs, retained between said block and said holder support. This arrangement has the advantage that the holder can be closed tightly by pushing the block against the resilient bias, and this can be done by means such as a solenoid or an air cylinder.
Preferably, the block is retained on the holder support by bolts passing through the block and engaging in the holder support, the block being biassed outwardly by the resilient means, and the bolts retaining the block on the holder support against the resilient bias and thus serving to define the open condition of the block, which can be varied by tightening or loosening the bolts. When the block is in its open position, it is biassed away from the recess, and so the distance between the block and the recess is a maximum. This is the position where the tube will preferably be loosely held in the holder. The bolts can be tightened or loosened to change this spacing, for example to accommodate thicker or thinner tubes, which may be needed to make different types of capsule.
The spacing between the block and the recess is important, as it must be large enough to allow the tube to easily enter the holder, but sufficiently small to ensure that the tube is held as required. In particular, the tube must be held in such a way as to ensure that when the holder is closed tightly around it, it is in the correct position for welding. The spacing can be set by inserting a gauge member of known thickness into the gap and tightening the bolts until the jaws just contact the gauge member, but this is an awkward procedure and does not guarantee that the bolts will not be over tightened. Accordingly, it is preferred that a set screw is provided in said recess, said set screw defining a point beyond which said bolts may not be tightened. This ensures that the spacing of the block and the recess is set correctly.
Provision of the set screw to ensure correct spacing of the block and the recess is also considered to be of inventive merit, and so according to a further aspect of the invention there is provided an automated method of welding closed one end of each of a multiplicity of open-ended tubes suitable for use as brachytherapy capsules, comprising repeating the steps of receiving a tube in a holder mounted on a holder support, conveying the tube past a welding station where one end of the tube is welded closed in a welding operation, and releasing the welded tube, said holder being in the form of a block slidably mounted in a recess on the holder support and retained on said holder support by bolts passing-through said block and engaging in said holder support, said block being biassed outwardly by resilient means acting between said block and said holder support, said bolts retaining said block on the holder support against the resilient bias and thus serving to define an open condition of the block, said open condition of said block being variable by means of tightening or loosening said bolts, and wherein a set screw is provided in said recess to define a point beyond which said bolts may not be tightened.
Since the holder will hold the tube while it is being welded, it is necessary for the holder to be formed from a material which has sufficient heat-resistance. It is preferred that the or each holder is formed from Elkonite. This material, an alloy of tungsten and copper, has good heat-resistance, but is easier to work than tungsten itself.
It is also preferred that the holder support, e.g. rotatable member, is formed from Elkonite.
The invention also extends to apparatus for carrying out the methods for welding closed one end of each of a multiplicity of tubes for use as brachytherapy capsules as described above.